Method for extracting nylon from waste materials

Abstract

The invention relates to a method for recovering nylon from a nylon-containing material by contacting the nylon-containing material with an alkanol-containing solvent at elevated temperature and at a pressure higher than the equilibrium pressure of the alkanol-containing solvent at the elevated temperature, thereby dissolving the nylon in the alkanol-containing solvent, removing the alkanol-containing solvent containing dissolved nylon from any undissolved solids, and decreasing the temperature of the alkanol-containing solvent containing dissolved nylon to precipitate the dissolved nylon.

Description

[0001]This application claims benefit of provisional U.S. application Ser. No. 60 / 245,006, filed Nov. 1, 2000, the entire contents of which are incorporated by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to improved processes for extracting nylon from waste materials, including mixed waste materials such as floor coverings, such that degradation of the nylon polymer into lower molecular weight polymers, oligomers, and monomers is decreased. The process involves contacting the waste materials with polar solvents, or mixtures thereof at high pressures.[0004]2. Description of Related Art[0005]Nylon is widely used as a fiber, both in the production of textile cloths, and in the production of floor covering materials, such as broadloom carpet and carpet tile. When used in floor covering materials, the nylon is usually predominantly present as part of one or more layers of a multilayered product. Large quantities of floor coverin...

AI Technical Summary

Benefits of technology

[0012]The process of the invention fulfills this need. Nylon, which may be obtained in the form of waste material, such as waste or scrap floor covering material (obtained, e.g., from used carpet, carpet tile, or other floor covering, or as selvedge produced in the manufacture of carpet or carpet tile), is contacted with a solvent or solvent mixture containing an alcohol at an elevated temperature, and at an elevated pressure. The use of an elevated pressure has been found to unexpectedly decrease the temperature at which the nylon in the waste material will effectively dissolve in the solvent mixture. At least in part as the result of this decrease in dissolution temperature, the nylon can be dissolved with a substantially decreased degradation of its molecular weight. This preservation of molecular weight allows the process to be effectively used with nylon that has been extruded into fiber, such as that found in floor coverings, and produces nylon that can again be extruded into fiber, for use in floor coverings. In effect, the process of the invention allows the nylon present in floor coverings to be recycled without being downcycled. Although the process can be used with nylon that has been separated from other composite material components, this need not occur with commonly used floor covering materials.

[0017]The increase in pressure of the nylon and alkanol-containing solvent mixture can be accomplished by introducing inert gas into the dissolution vessel, which is desirably a pressure vessel. Alternatively, the increase in pressure of the solvent mixture can be accomplished by increasing the head pressure of the solvent mixture pumped into the reactor. For instance, the vessel through which solvent is introduced to the reactor could have a cross-sectional area that exceeds that of the vessel through which solvent is withdrawn from the reactor, creating a pressure head in the reactor sufficient to lower the nylon dissolution temperature, and thus the reactor temperature, as described herein.

[0018]The method of the invention is suitable for recovering nylon from waste materials, and is particularly suitable for use with nylon-containing floor covering waste materials, such as used or scrap carpet or carpet tile, or selvedge obtained during production of these materials. In particular, use of the method with carpet tile has been found to be very beneficial, since these materials are typically composite structures having a number of laminated layers. The method of the invention provides the additional benefit of making separation of these laminated layers easier, and in many cases the waste materials emerge from the dissolution process with the nylon removed and the remaining layers of materials already separated. This confers apparent advantages in making the recycling of these additional components much more efficient.

Problems solved by technology

The use of an elevated pressure has been found to unexpectedly decrease the temperature at which the nylon in the waste material will effectively dissolve in the solvent mixture.